Hidden beneath the streets of London is a secret subway that only carried mail.

An abandoned Gold Coast-era mansion once intended for the exiled ruler of Albania, who never arrived.

Opulence and fantasy collide in this royal chair which is supposedly made with unicorn horns.

An exhibition of preserved locomotives housed in a 1950s depot shows the history of Denmark's railway.

These mysterious circular formations are actually remnants of 19th century gristmills.

A Chinese meditation center in the middle of rural Sweden, partly funded by a member of ABBA.

A natural wonder in south Denmark.

Public access to clean drinking water was an instant hit among the masses.

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

The largest of London's subterranean rivers and once a mad, bad center of London life.

The only university zoological museum in London houses extinct animals, bizarre natural history specimens, and a Micrarium of microscopic creatures.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

A toy store with a century-long history preserves the craftsmanship of playthings of the past.

The quaint little store that is said to have inspired a famous Dickens novel was only given its name after the book was released.

A naturally mummified 2,000-year-old man.

A collection of comics, graphic novels, animation and caricatures devoted to exploring this often overlooked art form.

Residential building on the Regents Canal is a breeding ground for creativity and innovation.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

A hands-off space for graffiti artists to hone and display their skills.

A modern artist's primitive stone faces and unique rock instrument join Iceland's terrain with its history.

This mountain fissure hides a secret path to a secluded mossy grotto within the rock itself.